Replacing the injector connector housings is very simple, once the upper intake is off. Replacing the engine wiring harness is simple, but not necessarily easy. You have to remove the connectors from the ECU under the glovebox, feed it though the firewall and then unplug the engine sensors as well as the two transmission harness junction connectors. IMO, these two are the hardest to get at. They sit on the frame above the starter.
You will also likely have trouble with the connectors in the head, unless you also remove the lower intake. IME, you can't unplug any of them with lower intake installed (unless they are new and clean and were lubed before they were connected) - you can't even see them. Unfortunately, this is a Hobson's choice because, unless your lower housing has been modified, the engine harness is fed through it, requiring you to unplug it before it can be removed. This is one of the reasons it's advisable to pull the engine when replacing a headgasket. There's no room to work on the driver's side of the engine (yes, it can be done, but there still isn't enough room there).
The knock sensor connector housings, as well as the sensors, are notorious for dissolving in your hands. My A/C cutoff sensor connector housing latch broke and I spent a week trying to find a solution (the housing is NLA).
There is no way I'd replace an entire harness for one, or even all of the, injector connector housing(s).
